1. Field of the Invention
The present invention relates to a method and device for cooling an insulated wire, that is, a coated wire in manufacture thereof.
2. Description of the Related Art
FIG. 17 shows a conventional insulated wired manufacturing equipment for coating a conductive core wire with an insulating material such as synthetic resin or the like. As shown, the insulated wire manufacturing equipment includes a core wire feeding device 31, a drawing device 32, a core wire softening device 33, a core wire pre-heating device 34, an extruder 35 having a cross head for coating a core wire with an insulating material at the extreme end, a cooling device 36 for cooling a coated wire, a dancer roller device 37, and a winder 38, wherein the above devices are disposed in a line in that order.
In this insulated wire manufacturing equipment, the cooling device 36 includes a water storage tank 39 movable in the wire advance direction, main water tank 41 containing a plurality of shower nozzles 40, and a cooling capstan 42 for air cooling. In this cooling device 36, a coated wire 43 fed from a conventional extruder 35 is made to pass through still water in the water storage tank 39 while being dipped therein, to be thus rapidly cooled. After that, it is further cooled by water sprayed through shower nozzles 40 and is then air-cooled at the cooling capstan 42. Accordingly, the coated wire is first cooled in the water storage tank having the largest cooling effect, after which it is further cooled in the order of weakening effect on cooling.
The reason why the water storage tank 39 having the largest cooling effect is first disposed among the above cooling means is as follows: namely, it has been considered that an insulating material formed on the surface of the coated wire 43 fed from the extruder 35 must be early solidified for preventing the insulating material from being peeled in a process of being wound around the winding means such as the cooling capstan 42 and the dancer roller device 37.
However, as the demands for finer insulated wires and the high production rate thereof has been enhanced, the conventional manufacturing equipment has encountered in the following problem: for example, in manufacturing fine wires having a coated outside diameter of 1 mm or less, the surface roughness often exceeds 10 .mu.m, and consequently, in a process of twisting the number of coated wires, they are rubbed with each other thereby causing cutting-off of the coated surfaces, further in the very worst case, they are reduced in the coated amounts in the degree of exerting adverse effect on the insulating property.
The present inventor has examined and found the fact that such deterioration of the surface roughness is due to the above-mentioned cooling device 36, especially, the water storage tank 39 constituting the rapid cooling stage. Namely, the rapid cooling of the coated wire 43 in the water storage tank 39 is required for solidifying the surface: however, the rapid cooling causes huge thermal shock. In a fine coated wire, such thermal shock causes a thermal stress difference between the core and the coating material, which makes the surface roughness larger in the non-negligible degree.